Durable optical fiber ribbons and methods of making optical fiber ribbons

ABSTRACT

Durable optical fiber ribbons are formed by promoting a strong bond between fiber ink layers and ribbon matrix material. During curing of the ink layer desired oxygen levels are maintained in the curing environment of the manufacturing process.

PRIORITY APPLICATION

This application is a continuation of International Application No.PCT/US10/51300 filed Oct. 4, 2010 which claims the benefit of priorityto U.S. Provisional Application No. 61/249,332, filed Oct. 7, 2009, bothapplications being incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to compositions for fiber optic ribbonmatrix materials and fiber optic ribbons that contain a matrix preparedfrom such compositions.

BACKGROUND

Optical fibers have acquired an increasingly important role in the fieldof communications, frequently replacing existing copper wires. Thistrend has a significant impact in local area networks (i.e., forfiber-to-home uses), which has seen a vast increase in the usage ofoptical fibers. Further increases in the use of optical fibers in localloop telephone and cable TV service are expected, as local fibernetworks are established to deliver ever greater volumes of informationin the form of data, audio, and video signals to residential andcommercial users. In addition, use of optical fibers in home andcommercial business environments for internal data, voice, and videocommunications is expected to increase.

Optical fibers are often bundled together to form an optical fiberribbon. The ribbon includes side-by-side and parallel optical fibersthat have been encased or encapsulated in a polymeric matrix material.The matrix portion of the optical fiber ribbon can include one or morelayers of the polymeric matrix material, and each optical fibertypically contains a dual layer coating system that includes a soft,inner polymer coating and a hard, protective outer polymer coating.Prior to forming the ribbon, the optical fibers may also be coated witha thin colored layer of marking ink (i.e., in a polymer base) forpurposes of fiber identification within the ribbon.

While the most basic function of the matrix materials is to secure theindividual optical fibers or ribbon sub-units in a planar array, theyalso contribute to the handling properties of the ribbon. Two importanthandling attributes of conventional optical fiber ribbons are peel andbreakout performance. Peel is the removal of matrix material from theoptical fibers in either the mid-span region or the end of the opticalfiber ribbon. It is considered desirable, for example, to be able topeel the matrix layers cleanly off the optical fibers without removingany of the colored marking ink layers. In addition, the matrix layersshould be removable as an intact unit without breaking apart and leavingresidue on the optical fibers. Breakout occurs at the ends of theribbons and is used to provide access to individual fibers in a ribbon.As with peel, it is desirable to be able to remove all fibers withoutdamage from the matrix material during breakout without it breakingapart and leaving residue on the optical fibers.

Conventional ribbon products have some degree of peel and breakout fiberaccess. There are various methods, designs and tools available to accessfibers, and all require some limited or controlled “bond” between thefibers and the ribbon bonding matrix material. This bond is typicallycontrolled by proper selection and design of the UV ink and matrixmaterials. The curing of the fiber ink color layer in an inertenvironment is also a requirement. The goal of the inert environment isto significantly reduce oxygen levels while curing (typically this isless than about 100 parts per million (ppm) oxygen in a nitrogen baseenvironment). Oxygen, if present during curing at levels above about 100ppm, will react with the free radicals formed for chain propagation andessentially stop the reaction at the outer surface of the ink colorlayer. In contrast, curing with an oxygen content at less than about 100ppm provides a controlled bond between the fibers and the ribbon matrix,but ultimately reduces the toughness or durability of the ribbon. Forexample, when the ribbon is incorporated into a cable and pulled throughtortuous paths and/or twisted, portions of the ribbon matrix mayseparate from the fibers and/or fracture at locations of high stress.“Twist failure” and other forms of ribbon damage may increaseattenuation or even cause fibers to go dark.

SUMMARY

According to one embodiment, a multi-fiber ribbon has colored fiberswith a secure bond to the ribbon matrix. The bonding yields a ribbonstructure that is extremely robust and which can be calibrated toprevent individual fiber access.

According to one aspect, secure or permanent bonding is achieved byreducing the cure on the surface of the ink using oxygen levels greaterthan about 100 ppm when initially curing the colored ink. The colorlayers of one or more fibers are cured with a desired level of oxygen sothat the color layer has a predefined level of surface cure. The fibersmay then be further cured in a conventional manner using, for example,UV light to undergo further cross-linking of the color layer. Ribbonscured in this manner have higher toughness than conventional ribbons.For example, the ribbon has a higher twist to failure point, highercrush resistance and has higher resistance to delamination at theink/matrix layer boundary than conventional ribbons.

While ribbons according to the present embodiments can be calibrated tobe unsuitable for individual fiber access without damage to the inklayers or the fibers, they may have superior thermal strip properties.The fibers in the ribbon can accordingly be thermally stripped as a unitand mated as a unit to a multifiber connector, for example.

It is to be understood that both the foregoing general description andthe following detailed description present embodiments of the invention,and are intended to provide an overview or framework for understandingthe nature and character of the invention as it is claimed.

BRIEF DESCRIPTION OF THE FIGURES

The present embodiments are explained in more detail below withreference to the figures which show the exemplary embodiments;

FIG. 1 is a cross-section of an optical fiber ribbon according to anembodiment of the present invention;

FIG. 2 is a schematic illustration of an ink layer application process;

FIG. 3 illustrates a device for testing twist properties of opticalfiber ribbons;

FIG. 4 illustrates crush testing of an optical fiber ribbon;

FIG. 5 illustrates optical fiber ribbons undergoing varying degrees oftwist;

FIG. 6 is a schematic illustration of an optical fiber ribbonfabrication process according to an embodiment of the present invention;and

FIG. 7 is a cross-section of an elliptical reflector curing lamp systemaccording to an embodiment of the present invention.

DETAILED DESCRIPTION

The present embodiments relate to optical fiber ribbons and methods ofmaking such ribbons. Oxygen inhibition is the effect of oxygen on thecuring process which terminates or retards the rate of polymerization.

FIG. 1 is a cross-section of an optical fiber ribbon 10 incorporatingmatrix materials according to the present embodiments. The optical fiberribbon 10 includes a plurality of substantially aligned optical fibers20 that are surrounded by and encapsulated within a ribbon matrix 30.Each of the optical fibers 20 includes a glass fiber having one or morecoatings (not shown). The ribbon matrix 30 can be either a single layermatrix or a dual layer matrix (formed of inner and outer matrixmaterials). In the illustrated embodiment, the matrix 30 includes aninner matrix 34 and an outer matrix 38. The inner matrix 34 surroundsand contacts the optical fibers 20, and the outer matrix 38 surroundsand contacts an outer surface of the inner matrix 34.

Each of the optical fibers 20 includes a colored ink coating layer 40 toallow for identification of individual optical fibers 20. The exemplaryoptical fiber ribbon 10 shown in FIG. 1 includes twelve optical fibers20 arranged as a 1×12 ribbon. The colors for the colored ink coatinglayer can be a 12-color sequence of blue, orange, green, brown, slate,white, red, black, yellow, purple, rose, and aqua. The 1×12 ribbon mayhave a thickness 44 at its midsection in the range of, for example, fromabout 250 to about 330 microns. In the illustrated embodiment, the bondbetween the ink layers on the fibers and the matrix is calibrated suchthat the fibers are not individually accessible without damaging thefibers or the ink layers.

FIG. 2 is a schematic diagram of a coloring line used to color a fiberto be incorporated into an optical fiber ribbon according to the presentembodiments. In an exemplary process, an uncolored coated optical fiber100 is paid off from a fiber payoff 102 and passed through an ink head106 where a selected ink color is applied to the fiber 100. For atwelve-fiber ribbon as shown in FIG. 1, each fiber 20 can be coated withink individually, or multiple fibers can be colored in a single device.In an exemplary embodiment, the fibers 20 are coated individually,stored on separate spools, and then moved to a matrix applicationprocess. The ink composition used to color the fibers can be, forexample, ink compositions as described in U.S. Pat. Nos. 7,257,299 and7,289,706, the contents of both patents being hereby incorporated byreference in their entirety. Other ink compositions are also suitable.The ink can be applied at a thickness in the range of, for example, fromabout 1 to about 10 microns, or more specifically, in the range of fromabout 2.5 to about 7 microns.

The colored but uncured optical fiber 110 then passes to a curingstation 112. The curing station 112 includes a curing gas supply 114.The curing gas supply 114 provides a mix of nitrogen (N₂) and oxygen(O₂) gases, wherein the oxygen levels supplied to the curing process arehigher than in conventional processes. The flow rates of the N₂(typically 99.999% pure) and compressed air, which is about 21% O₂, arecontrolled using conventional flow meters and pressure regulators. Theflow rates of the various gases are regulated and adjusted to achievethe desired O₂ level in the curing zone. The various gases can beprovided from separate sources or from a single source. In accordancewith the present embodiment, the level of O₂ gas supplied from thecuring gas supply 114 to the curing zone is higher than the conventionallevel of about 100 ppm in a nitrogen base environment. The O₂concentration can be, for example, at least about 1,000 ppm, preferably,at least about 5,000 ppm and more preferably, at least about 10,000 ppmin the curing zone. Preferably, the O₂ concentration can be from about5,000 to about 210,000 ppm, more preferably from about 10,000 to about100,000 ppm, most preferably from about 30,000 to about 70,000 ppm, andstill more preferably about 50,000 ppm.

According to one embodiment, atmospheric air can serve as the curinggas. Atmospheric air, having an O₂ concentration of about 210,000 ppm,enables a strong bond between ink and matrix. The use of atmospheric airmay be preferred because compressed air is relatively inexpensive anddoes not require handling of compressed O₂.

In the curing station 112, the colored uncured fiber 110 is advancedpast two curing lamps 120, 124 that provide ultraviolet (UV) radiationto cure the ink applied to the fiber exterior. The presence ofrelatively high levels of oxygen in the ink curing process acts toinhibit curing on the surface of the ink layer. A conventional O₂ levelmonitor 128 can be included in the curing gas supply 114 to maintain theoxygen at desired levels. There are therefore cure-inhibited sites onthe ink surface that can continue chain propagation when another layerof free radical curing material, such as matrix material, is placed incontact with the ink layer during, for example, a ribbonization process.

The colored and cured optical fiber 134, which generally corresponds tothe fibers 20 shown in FIG. 1 before they are ribbonized, is then takenup around a capstan 140 and onto a fiber take-up spool 144 for use in aribbonization process.

Fibers colored in accordance with the methods described herein can beincorporated into ribbons using known ribbonization processes and knowninner and outer matrix compositions. According to the presentembodiments, the matrix 30 comprises UV-curable ribbon matrix materials.For example, the inner matrix 34 can be formed from compound DSM 950-706available from DSM Desotech, Inc. The outer matrix 38 can be formed fromcompound DSM 9D9-518. Other known matrix materials are also suitable.The inner and outer matrix materials can be cured using conventionalprocesses. Because of the presence of the cure-inhibited portions of theink layers of the fibers 20, when the inner matrix 34 material isapplied to the fiber and subjected to UV irradiation, the uncuredportions of the ink crosslink with the inner matrix material to create astrong bond between the ink and the ribbon matrix. The UV radiation mayalso serve to cure uncured portions of the ink.

According to the above-described method, a durable ribbon having highrobustness and toughness can be produced using conventional apparatuses.

FIG. 6 is a schematic diagram of a ribbon line used to join multipleoptical fibers into a bonded array. In this example, 12 individualcolored and cured optical fibers 202 on individual spools 201 are paidoff and passed through a tool 203. A ribbon bonding material or matrix204 is applied while the fibers are arranged in a linear array. Thecoated linear array of colored fibers 209 is passed through a UV lamp205 to cure the matrix. Nitrogen 206 is used in this curing to allowrapid cure on the surface and thus, form a non-sticky surface. Duringcuring of the matrix material, the ink layer undergoes furthercross-linking to create a strong bond between the ink and the ribbonmatrix. The ribbon is pulled through the process at a controlled rate bya capstan 207 and the ribbon is put on a take-up reel spool 208 forstorage. This bonded array of colored fibers is called a ribbon.

FIG. 7 is a cross-section of the elliptical reflector curing lamp system400 for curing the color layer on the optical fiber. The ellipticalreflector curing lamp system 400 is a subsystem located in each of thelamps 120 and 124 of FIG. 2. This system is typically made of two halfreflectors, a primary reflector 403 which has the UV bulb 401 located atone foci point and a secondary reflector 404 which has a quartz tube 402encircling the other foci point. The quartz tube 402, or any othermaterial that transmits UV light to the cure zone, provides a seal forthe controlled curing environment (N₂ and O₂ mixture). The colored fiberpasses through the center of the quartz tube 402 in the cure zone 405and the UV light cures the ink layer. The cure zone 405 diameter istypically less than or equal to the inside diameter of the UV bulb 401.

According to the above embodiments, ribbons can be produced of superiortoughness and resistance to delamination. The ribbons also have hightwist to failure points and crush resistance. Ribbons produced accordingto the methods discussed herein may be calibrated to prevent individualfiber access, but have superior thermal strippability.

EXAMPLES Example 1 Coloring Process Parameters

The ink applied to the fiber is formulated so as to be hardened or curedby exposure to UV light. UV light of desired wavelength will providesufficient energy to initiate a free radical reaction which willcross-link the liquid ink into a hardened ink layer. After the ink layeris applied by ink head 106 to an optical fiber 100, the colored uncuredfiber 110 enters a UV curing lamp 120 in the curing zone 112 of FIG. 2.The speed at which any UV curable material can be processed is relatedto the total UV exposure. In the curing of optical fiber and inkedoptical fiber the curing speed is typically a function of the curinglamp, bulb type, bulb size and system power. The present examples usedthe following curing conditions. The ink was applied to a thickness offrom 3 to 10 microns. The line speed was 1500 m/min. 2 Fusion 6000 wattlamps were used in curing station 112 of FIG. 2. Each of the lamps 120and 124 contained focused elliptical reflectors 400, as shown in FIG. 7.Each of the Fusion lamps were 600 watt/in. lamps having 10″ long 11 mm Dbulbs. The resulting UV exposure to the fiber was equal to 20.3 msec.

Matrix peel qualities can be evaluated and quantified using a matrixpeel test. One procedure for testing peel is as follows: 1. using aroughly 12 inch sample of ribbon 10, hold the top end of the ribbon withthe thumb and index finger about 1 inch from the end and twist theribbon end 90° in one direction and then 90° in the other direction—thematrix material 30 should break loose from the fibers 20; and 2. graspthe matrix layer 30 on one side of the ribbon and pull down to removethe matrix 30 from the fibers 20. Rate the peel according to the scaledetailed in Table 1.

TABLE 1 Peel Rating Scale: Ribbon applied to carpet tape on peel boardRating Rating Criteria 1 All coating peels cleanly the full length fromboth sides of the ribbon and no residue on any fiber. 2 All coatingpeels cleanly the full length from both sides of the ribbon but residueremains on the edge fiber that can be easily removed. 3 The coatingpeels cleanly on one side only. 4 The coating can only partially bepeeled from either side 5 The ribbon coating will not peel from theribbon.

Breakout qualities for a 12 fiber ribbon undergoing fiber breakout forthe first fiber can be evaluated and quantified using the followingprocedure: 1. using a roughly 18 inch ribbon 10 sample, hold the top endof the ribbon 10 with the thumb and index finger at about 1 to 2 inchesfrom the end of the ribbon 10 and twist the ribbon end 90° in onedirection and then 90° in the other direction—the matrix material 30should break loose from the fibers 20; 2. remove the end fiber andremove any matrix 30 from the end fiber; and 3. grasp the remaining 11fibers 20 with one hand and hold the matrix 30 with the other hand andattempt to remove the 11 fibers 20 all at once. When all the fibers havebeen removed, examine the matrix 30 for damage and rate the 12 fiberbreakout performance according to the rating scale detailed in Table 2.

TABLE 2 12 Fiber Breakout Rating Scale Rating Rating Criteria 1 Fiberswere easily removed, matrix shell is undamaged. 2 Fibers were removedwithout damage to the matrix shell, but the matrix separates into 2strips. 3 Fibers were removed from the matrix, but the shell is damagedwith several spots where the matrix stuck to the fibers. 4 Fibers wereremoved from the matrix, but the shell was significantly damaged withlots of areas where the matrix stuck to the fibers, or the matrix isshredded. 5 Fibers cannot be removed from the matrix.

Single fiber breakout qualities for a 12 fiber ribbon can be evaluatedand quantified using the following procedure: 1. using a roughly 18 inchribbon 10 sample, hold the top end of the ribbon 10 with the thumb andindex finger at about 1 to 2 inches from the end and twist the end 90°in one direction and then 90° in the other direction. The matrixmaterial 30 should break loose from the fibers 20; 2. remove the endfiber and remove any matrix 30 from the end fiber 20; and remove theremaining fibers 20 one at a time. Rate the overall single fiberbreakout of the ribbon 10 according to the rating scale detailed inTable 3.

TABLE 3 Single Fiber Breakout Rating Scale Rating Rating Criteria 1Fibers remove easily from matrix and matrix stays in a cohesive shell. 2Fibers release from matrix in a jerky fashion, however, matrix forms acohesive shell. 3 Fibers remove easily from matrix, but shell separatesinto two strips. Some flaking of the matrix shell may occur. 4 Matrixadheres to at least one fiber, other than end fiber, during breakout. 5Cannot remove fiber from the matrix. Color layer is removed or fiberbreaks.

Example 2 NPR Performance by O₂ Level

No peel ribbons (NPR) are defined as ribbons that will not peel or havefiber access (during either 12 fiber breakout or single fiber breakouttesting). A rating of 5 indicates the ribbon will not peel or allowfiber breakout. This rating is consistently achieved by ribbons preparedwhen the oxygen level during curing of the coloring layer is 10,000 ppmor greater, as shown in the table below. However, satisfactory resultscould be achieved by ribbons prepared when the oxygen level duringcuring of the coloring layer is between about 1,000 and about 10,000 ppmdepending on material and processing conditions. These effects can beoptimized by reducing the cure dose to the fiber, for example, byincreasing the line feed, reducing the lamp intensity, or modifying thematerial composition, for example, by increasing the photoinitiatorconcentration, and the like.

NPR prepared in accordance with the present embodiments show improvedpeal and breakout performance over standard peel ribbons (SPR) preparedin accordance with the prior art, as shown in the table below. Moreover,at oxygen levels of 100,000 ppm during curing of the coloring layer caremust be taken to avoid processing problems in removing the fibers fromthe reel.

Average of 5 Ribbon Samples O₂ (ppm) Peel Rating Breakout Rating <100 ≦2≦2 1,000 4.17 3.25 10,000 5.00 5.00 25,000 5.00 5.00 50,000 5.00 5.0075,000 5.00 5.00 100,000 5.00 5.00 NPR should always have ratings of 5

Example 3 NPR Twist Performance

FIG. 3 illustrates a device for measuring the twist properties ofoptical fiber ribbon. FOTP-141 is a known standard that measures twistcycle properties of ribbons. FOTP-141 states that a 300 mm long sampleof ribbon must withstand 20 cycles at 15 to 20 twist cycles per minute.A cycle consists of rotating the ribbon 180° clockwise, 360°counterclockwise, then 180° clockwise. In a twist-to-failure test, aribbon sample is loaded on the twist bench and twisted about itself inone direction until the matrix fails. Failure is detected by the loadcell and the failure rotation point is recorded by a computer. Forribbons, failure can be detected as delamination of the matrix/colorinterface or matrix breaking between two fibers.

NPR prepared in accordance with the present embodiments show improvedtwist performance over SPR prepared in accordance with the prior art, asshown in the table below. The resulting increased twist-to-failure (TTF)is consistent over temperatures of from 135° C. to 175° C. for up to 30minutes.

All NPR in the table below were manufactured using 50,000 ppm oxygenduring curing of the coloring layer.

Twist per 305 mm Time Temperature (min.) NPR SPR Unaged 0 10.01 7.23135° C. 5 9.88 6.52 15 9.81 6.93 30 9.67 7.04 135° C. Average 9.79 6.83155° C. 5 9.74 6.66 15 9.54 7.09 30 9.49 6.87 155° C. Average 9.59 6.87175° C. 5 9.76 7.03 15 9.76 6.95 30 9.63 7.28 175° C. Average 9.72 7.09

FIG. 5 illustrates ribbons undergoing varying numbers of twists. Ribbonsproduced according to the present embodiments are capable of undergoingup to nine or ten twists over a 300 mm length of fiber without signs offailure.

Example 4 NPR Crush Performance

The NPR show improved Crush performance over SPR prepared in accordancewith the prior art, as shown in the table below. The resulting increasedCrush performance is consistent over temperatures of from 135° C. to175° C. for up to 30 minutes.

All NPR in the table below were manufactured using 50,000 ppm oxygenduring curing of the coloring layer.

Average of Ribbon Crush Temperature Time (° C.) (min.) NPR SPR InitialUnaged 322 261 135 5 370 261 15 304 248 30 300 247 155 5 374 288 15 357302 30 356 194 175 5 340 259 15 302 237 30 323 249 Total Average 335 255

FIG. 4 illustrates a method of crush testing ribbons. In the crush test,two plates with a slot for the ribbon are mounted on an Instron machine.A constant strain is applied and failure occurs when the force or loadsuddenly drops.

The foregoing is a description of various embodiments that are givenhere by way of example only. Although matrix materials have beendescribed with reference to preferred embodiments and examples thereof,other embodiments and examples may perform similar functions and/orachieve similar results. All such equivalent embodiments and examplesare within the spirit and scope of the disclosure and are intended to becovered by the appended claims.

1. A method of forming an optical fiber ribbon, comprising: providing anoptical fiber; applying a colored ink layer to the optical fiber; curingthe colored ink layer in a curing environment having an Oxygen (O₂)content in an amount of at least 5,000 parts per million (ppm) to form acured colored optical fiber; applying a ribbon matrix material over thecured colored optical fiber and additional optical fibers; and curingthe ribbon matrix material to form a ribbon matrix in which the opticalfibers are embedded.
 2. The method of claim 1, wherein the O₂ content ispresent in the curing environment in an amount of between 10,000-100,000ppm.
 3. The method of claim 1, wherein curing the colored ink layercomprises providing atmospheric air to the curing environment.
 4. Themethod of claim 1, wherein curing the ribbon matrix material comprisesirradiating the matrix material with ultraviolet radiation.
 5. Themethod of claim 1, wherein providing an optical fiber comprisesproviding a coated optical fiber.
 6. The method of claim 1, whereincuring the colored ink layer comprises monitoring the Oxygen content. 7.The method of claim 1, wherein the ribbon matrix comprises an inner andan outer matrix.
 8. The method of claim 1, wherein the optical fibersare aligned in parallel.
 9. The method of claim 1, wherein the coloredink layer is applied at a thickness in the range of 1-10 microns. 10.The method of claim 1, wherein the ribbon matrix has a thickness of250-330 microns at its midpoint.
 11. A method of forming an opticalfiber ribbon, comprising: providing a plurality of optical fibers;applying a colored ink layer to at least one of the optical fibers;prior to curing the colored ink layer, applying a ribbon matrix materialover the optical fibers; and curing the ribbon matrix material.
 12. Themethod of claim 11, wherein providing a plurality of optical fiberscomprises providing coated optical fibers.
 13. The method of claim 11,wherein the ribbon matrix material is applied as an inner and an outermatrix.
 14. The method of claim 11, wherein the optical fibers arealigned in parallel.
 15. The method of claim 11, wherein the colored inklayer is applied at a thickness in the range of 1-10 microns.
 16. Themethod of claim 11, wherein the ribbon matrix material has a thicknessof 250 to 330 microns at its midpoint.
 17. An optical fiber ribbon,comprising: a plurality of optical fibers aligned in parallel; aplurality of ink coloring layers, one coloring layer on each opticalfiber; and a ribbon matrix surrounding and encasing the optical fibers,wherein individual optical fibers cannot be accessed from the ribbonmatrix without damaging the fiber.
 18. The optical fiber ribbon of claim17, wherein the ribbon matrix comprises an inner and an outer matrix.19. The optical fiber ribbon of claim 17, wherein the ribbon matrix hasa thickness of 250 to 330 microns at its midpoint.
 20. The optical fiberribbon of claim 17, wherein individual optical fibers cannot be accessedfrom the ribbon matrix without damaging the ink coloring layer on thefiber.